Think of it this way, the verb 'be' is a state verb and shows the state of something now. E.g. "I am hungry". We use "get" instead of "be" when showing a change from one state to another: "I wasn't hungry before, but I am now. I got hungry because I skipped breakfast". Other examples are: Don't get lost. I got a new job. I got sick. Notice the change in state. We also have some phrases like "get by" meaning having just enough to accomplish something, e.g. "I know enough English to get by when travelling". Or "Get to" meaning having the opportunity to do something you really want to do, for example, "My friend has a spare ticket to my favourite band's concert, so I get to see them live!"